In the area of active protective apparel, a need exists for improved, lightweight, multifunctional garments and equipment which can be worn in changing environments for extended periods of time. A single unit or garment is desirable that is adaptable to a variety of challenges, reducing the necessity of carrying additional specialized units and meeting the requirements of low bulk and weight. Such a garment would be useful for emergency responders and military personnel, as well as for persons involved in other outdoor activities.
The provision of a microclimatizing garment capable of insulating against temperature extremes, while also maintaining comfort and health by promoting normal moisture evaporation from the skin, represents an advancement of the art both in terms of performance and simplicity of design. Other similar constructions rely on bulky or technically complex internal materials to provide the insulative or heat exchange function. For example, some garments rely upon an open-celled foam placed adjacent to the wearer's skin to act as both a thermal insulator and to promote static transport of moisture from the skin to a secondary absorbent layer. The breathability of such foam is limited. Further, the absorbent layer traps moisture and thereby lessens the wear-cycle time of the garment due to saturation and potential microbial growth in the absorbent layer.
Other state-of-the-art garments employ an insulative pocket that contains a phase-change, heat transfer material. Optimum functionality of this design relies upon the use of ice, also placed in pockets in the garment. Obviously, this design has limited utility as a field item and would be for short-term, acute use only.
Another design uses a bladder system having channels through which a fluid may be pumped. Within the channels of the bladder system, a solid ribbon of closed cell foam is placed to force the channel to maintain its desired shape to maximize the contact area of the channels against the skin of the wearer. In order to allow the fluid to flow in the channels, the channel walls must be expandable to allow the fluid to flow around the solid ribbon of closed cell foam. A pressure required to pump the fluid through such a system can cause problems. The pressure causes the garment to be more rigid than is desirable and puts a large stress in the channel walls. In such a system, only a liquid can be used effectively. Since the fluid must flow around the closed cell foam ribbon, at least part of the fluid will flow in the section of the channel above the ribbon of closed cell foam. This part of the fluid flow does not aid in the transfer of heat in relation to the wearer's body. By fulfilling the purpose of maintaining the desired shape of the channels, the closed cell foam ribbon can actually isolate that part of the fluid flow, rendering it useless. Further, the use of a solid ribbon of closed cell foam prevents the flow of the fluid if a crease occurs in the channel or the channel is compressed.